Introduction

Upgrading the intake manifold on a Honda Prelude is one of the most effective bolt-on modifications for unlocking substantial horsepower gains. The Skunk2 intake manifold is engineered to improve airflow and distribution, providing a noticeable increase in throttle response and top-end power. With careful installation and supporting modifications, owners have reported gains of up to 25 horsepower at the wheels. This guide covers every step of the process, from gathering the correct tools to final tuning considerations, ensuring you get the most out of your Skunk2 manifold without common installation mistakes.

Benefits of the Skunk2 Intake Manifold for the Honda Prelude

The Skunk2 intake manifold is designed specifically for H-series and F-series engines found in fourth- and fifth-generation Honda Preludes. Its larger plenum volume and optimized runner geometry reduce airflow restriction compared to the factory manifold. The result is improved volumetric efficiency, especially at higher RPMs, where the Prelude’s VTEC system can take full advantage of the increased flow. When paired with a free-flowing exhaust, cold air intake, and proper engine management, the 25-horsepower claim is realistic and repeatable. Beyond peak power, the manifold improves throttle response and mid-range torque, making the Prelude more enjoyable to drive daily or on the track.

Tools and Materials Required

Before beginning, gather all necessary tools and replacement parts. Using the correct equipment prevents damage to the engine and ensures a leak-free installation.

  • Skunk2 intake manifold – Ensure you order the correct version for your Prelude’s engine code (H22A, H22A4, F22B, etc.).
  • Socket set with extensions – 10 mm, 12 mm, and 14 mm sockets are most common for intake manifold bolts and throttle body fasteners.
  • Torque wrench – Critical for tightening manifold bolts to the manufacturer’s specification (typically 16–18 ft-lbs for H22 engines).
  • Screwdrivers – flathead and Phillips – For vacuum hose clamps and sensor connectors.
  • Gasket scraper or razor blade – To clean the old gasket residue from the engine block surface without scratching it.
  • New intake manifold gasket – Use a high-quality OEM or aftermarket gasket; never reuse the old one.
  • Throttle body cleaner and shop towels – Clean the throttle bore and idle air control passages while the manifold is off.
  • Rubber gloves and safety glasses – Coolant and fuel vapors may be present; protect your skin and eyes.
  • Coolant drain pan – Some coolant may leak from the throttle body coolant lines; draining the radiator slightly prevents mess.
  • Thread locker (medium strength) – Optional but recommended for manifold bolts if specified by Skunk2.
  • Dielectric grease – For electrical connectors to prevent corrosion.

Preparation Steps

Proper preparation saves time and reduces the risk of damaging components. Perform these steps before touching any bolts.

  • Park the vehicle on level ground and allow the engine to cool completely. A hot engine can cause burns and make gaskets difficult to remove.
  • Disconnect the negative battery terminal. This prevents accidental shorts, especially when working near fuel injectors or sensors.
  • Remove the engine cover (if equipped) and any plastic trim pieces that obstruct access to the intake manifold.
  • Drain about one quart of coolant from the radiator by opening the petcock into a clean container. This lowers the coolant level below the throttle body heater hoses, preventing a large spill when you disconnect them.
  • Take a photo of the vacuum line routing and sensor connector positions. Reference images are invaluable when reinstalling everything correctly.
  • Clean the engine bay around the intake manifold with a degreaser if it is heavily soiled. Loose dirt can fall into open ports during removal.

Removing the Stock Intake Manifold

Removing the original manifold requires patience and careful attention to attached components. Follow this sequence to avoid damage.

  1. Disconnect the air intake duct and mass airflow (MAF) or manifold absolute pressure (MAP) sensor if applicable. On OBD2 Preludes, the MAF sensor is attached to the intake tube; set it aside gently.
  2. Remove the throttle cable bracket and throttle cable from the throttle body. Use a wrench to loosen the locknuts, then slide the cable off. Do not bend the cable sharply.
  3. Disconnect the throttle body coolant lines. Place a drip pan underneath. Expect some coolant loss; have rags ready to absorb drips.
  4. Unplug all electrical connectors attached to the intake manifold: idle air control valve (IACV), throttle position sensor (TPS), intake air temperature sensor (IAT), and knock sensor. Press the release tabs carefully to avoid breaking clips.
  5. Remove vacuum lines one by one. Label them with masking tape and a marker. Pay special attention to the large vacuum line that goes to the brake booster.
  6. Remove the intake manifold support bracket (if present on your Prelude). This bracket runs from the manifold to the block; a 12 mm bolt secures it.
  7. Unbolt the intake manifold using the 12 mm or 14 mm socket. There are usually 8–10 bolts holding the manifold to the cylinder head. Start with the bolts on the outer edges, then work inward. Keep all bolts together in a labeled bag.
  8. Carefully lift the stock manifold away from the engine. It may stick to the old gasket; gently rock it back and forth. Avoid prying against the cylinder head with a metal tool.
  9. Clean the mating surface on the cylinder head using a gasket scraper and brake cleaner. Remove all traces of old gasket material and carbon. Use a plastic scraper if you are concerned about scratching the aluminum surface; any nicks can cause vacuum leaks.
  10. Stuff clean rags into the intake ports to prevent debris from falling into the engine while you work on the new manifold.

Installing the Skunk2 Intake Manifold

With the stock manifold removed, you can now install the Skunk2 unit. Precise torque and gasket alignment are critical for a reliable seal.

  1. Remove the rags from the intake ports and wipe the area again with a lint-free cloth.
  2. Place the new intake manifold gasket onto the cylinder head. Most Skunk2 gaskets have alignment tabs or holes that fit over locating dowels. Ensure the gasket is oriented correctly (e.g., the larger openings match the ports).
  3. Position the Skunk2 intake manifold over the gasket. Align the bolt holes carefully. Do not force the manifold down; if it does not seat evenly, check for misaligned gasket or vacuum line obstructions.
  4. Hand-tighten all manifold bolts in a crisscross pattern to seat the manifold evenly. This prevents warping the gasket.
  5. Torque the bolts to the manufacturer’s specification. For Skunk2 manifolds on H22 engines, the typical torque is 16–18 ft-lbs (22–24 Nm). Use a calibrated torque wrench and tighten in two stages: first to 10 ft-lbs, then to the final specification.
  6. Reinstall the intake manifold support bracket (if removed). Torque to 18 ft-lbs.
  7. Reconnect all vacuum lines following your reference photos. Pay attention to the brake booster line; a loose connection here causes a hard brake pedal.
  8. Reinstall the throttle body onto the Skunk2 manifold. Use a new throttle body gasket if your kit includes one. Tighten throttle body bolts to 16 ft-lbs (refer to your service manual).
  9. Reconnect the throttle cable. Adjust the cable so there is about 1 mm of free play at the throttle arm when the pedal is released.
  10. Reattach the coolant lines to the throttle body. Tighten hose clamps securely.
  11. Plug in all electrical connectors – IACV, TPS, IAT, knock sensor. Apply a small amount of dielectric grease to the terminals to prevent oxidation.
  12. Reinstall the air intake duct and any breather hoses that connect to the manifold.
  13. Refill the coolant system with the coolant you drained, plus a little extra to compensate. Run the engine with the radiator cap off until the thermostat opens and bubbles stop, then top off.

Post-Installation Checks and First Start

After the manifold is installed, perform these final checks before driving.

  • Reconnect the negative battery terminal.
  • Turn the ignition key to the ON position but do not start the engine. Listen for the fuel pump prime; check for fuel leaks around the fuel injectors if your manifold required injector removal.
  • Start the engine and let it idle. It may run rough initially as the ECU relearns the idle air control settings. Allow the engine to reach operating temperature.
  • Inspect for vacuum leaks by spraying carburetor cleaner around the manifold gasket and vacuum line junctions. If idle speed increases, you have a leak that must be fixed before driving.
  • Check for coolant leaks at the throttle body hoses and at the manifold’s coolant ports (if any). Tighten clamps as needed.
  • Verify throttle operation – the throttle should open fully when the pedal is pressed, and return to idle without sticking.
  • Perform a test drive at moderate RPMs. The first few miles should be gentle to allow the ECU to adapt. Avoid full-throttle pulls until the engine has completed a few drive cycles.

Tuning and Achieving the Full 25 HP Gain

The Skunk2 intake manifold delivers its maximum power increase when combined with proper engine management. The factory ECU has limited ability to adjust fuel and ignition maps for the increased airflow. To realize the advertised 25 horsepower gain, consider the following:

  • Aftermarket ECU or piggyback tuner – A Hondata S300, KPRO, or a standalone like AEM Infinity allows you to dial in fuel tables and ignition timing specifically for the manifold. Many tuners report 20–25 wheel horsepower after tuning.
  • Supporting modifications – The manifold works best with a high-flow intake, a larger throttle body (e.g., a Skunk2 68 mm or 70 mm throttle body), and a free-flowing exhaust header and cat-back system. These mods reduce overall restriction.
  • VTEC engagement point – With the increased top-end flow, you may want to adjust the VTEC crossover point to a slightly higher RPM (around 5200–5500 RPM) to take full advantage of the manifold’s tuning.
  • Dyno tuning – A professional dyno tune with wideband air-fuel ratio monitoring ensures safety and maximizes power. Without tuning, you may see only 10–15 HP, and the engine could run lean under full load.

Common Mistakes to Avoid

Even experienced mechanics can make these errors when installing an intake manifold.

  • Over-torquing the manifold bolts – This distorts the manifold or strips threads in the aluminum cylinder head. Always use a torque wrench.
  • Reusing old gaskets – A new gasket is cheap insurance against vacuum leaks. The old gasket has been compressed and may not seal properly.
  • Forgetting to reconnect the brake booster vacuum line – This causes a very hard brake pedal and is a safety hazard.
  • Ignoring the need for a tune – The engine may run okay, but you leave power on the table and risk detonation under load.
  • Leaving the throttle cable misadjusted – Too much slack reduces throttle response; too little can keep the throttle partially open, causing high idle.

Performance Expectations and Real-World Results

With the Skunk2 intake manifold installed and tuned, owners of Honda Preludes (especially H22A equipped) have documented peak power gains of 20–25 wheel horsepower on dynojet dynos. The torque curve remains flat in the mid-range and then rises sharply in the upper RPM band. Below are examples of supporting mods commonly paired:

  • Cold air intake (e.g., AEM, Injen)
  • Skunk2 68 mm throttle body
  • Aftermarket header (e.g., DC Sports, Kamikaze)
  • High-flow catalytic converter or test pipe
  • Cat-back exhaust (2.5-inch diameter)
  • Hondata S300 ECU tune

Without tuning, the gains are closer to 10–12 HP, but the manifold still improves throttle response and sound. The 25-horsepower figure is realistic for a fully optimized setup.

External Resources and Further Reading

For more technical specifications, installation videos, and community feedback, visit the following links:

Conclusion

Installing a Skunk2 intake manifold on your Honda Prelude is a rewarding modification that can deliver up to 25 extra horsepower when combined with proper tuning and supporting parts. By following the detailed steps outlined here—removing the stock manifold, carefully installing the new one, and ensuring all vacuum and coolant connections are correct—you can complete the job in an afternoon with basic hand tools. The key to unlocking the full potential lies in engine management: do not skip the tune. Whether you use a standalone ECU, a piggyback chip, or a professional dyno session, your Prelude will reward you with sharper throttle response, a more aggressive sound, and a noticeable power increase that makes every drive more exciting.